Fix issue with empty oauth_token

Set initial token reference to None to prevent sending empty
oauth_token string on temporary token requests.

Author: tnydwrds

ox3apiclient.py

@@ -50,7 +50,7 @@ def __init__(self, domain, realm, consumer_key, consumer_secret,
         # You shouldn't need to access the oauth2 consumer and token objects
         # directly so we'll keep them "private".
         self._consumer = oauth.Consumer(self.consumer_key, self.consumer_secret)
-        self._token = oauth.Token('', '')
+        self._token = None
 
         # Similarly you probably won't need to access the cookie jar directly,
         # so it is private as well.